A version of this article first appeared in CNBC's Inside Wealth newsletter with Robert Frank, a weekly guide to the high net worth investor and consumer. Sign up to receive future editions, straight to your inbox. Equity Group Investments, backed by the family of late billionaire Sam Zell, owns a John Deere dealership, a bluefin tuna fishery and a pedestrian bridge that connects San Diego to Tijuana International Airport. While those holdings sound entirely unrelated, what unites the private